US 20050280866 A1 Abstract In a set of non-reference gamma characteristics corresponding to a density adjustment value, a first region has first characteristics for converting input values to the maximum output value. A second region has second characteristics for converting input values to the minimum output value. A third region defined between the first and second regions has third characteristics for converting input values to intermediate output values. The third characteristics defines a monotonous curve that changes monotonously with respect to chance in the amount of the input value. The amount of at least one of the first region and the second region is different from the amount of the corresponding at least one of the first reference region and the second reference region of the reference gamma characteristics by a degree dependent on the each density adjustment value. The third characteristics is different from the third reference characteristics of the reference gamma characteristics in at least a partial range of the third region that is next to the at least one of the first region and the second region, the at least a partial range being determined dependent on the each density adjustment value.
Claims(24) 1. A density-adjusting device, comprising:
a density-adjustment-value setting unit that is capable of setting a density adjustment value, according to which a density of image data is desired to be adjusted with respect to a predetermined reference density value; a gamma characteristics storing unit that is prestored with a set of reference gamma characteristics in correspondence wish the reference density value and that is prestored with a plurality of sets of non-reference gamma characteristics in correspondence with a plurality of density adjustment values that can be set by the density-adjustment-value setting unit; and a correcting unit that corrects values of the image data by using one set of non-reference gamma characteristics that corresponds to the density adjustment value set by the density-adjustment-value setting unit, thereby adjusting the density of the image data according to the desired density adjustment value, wherein the set of reference gamma characteristics includes: a first reference region having first reference characteristics for converting input values to a predetermined maximum output value; a second reference region having second reference characteristics for converting input values to a predetermined minimum output value; and a third reference region defined between the first and second reference regions and having third reference characteristics for converting input values to intermediate output values defined between the maximum output value and the minimum output value, the third reference characteristics defining a reference monotonous curve that changes monotonously with respect to change in the amount of the input value, and wherein a set of non-reference gamma characteristics that corresponds to each density adjustment value includes: a first region having first characteristics for converting input values to the maximum output value; a second region having second characteristics for converting input values to the minimum output value; and a third region defined between the first and second regions and having third characteristics for converting input values to intermediate output values defined between the maximum output value and the minimum output value, the third characteristics defining a monotonous curve that changes monotonously with respect to change in the amount of the input value, the amount of at least one of the first region and the second region being different from the amount or the corresponding at least one of the first reference region and the second reference region by a degree that is determined dependent on the each density adjustment value, the third characteristics being different from the third reference characteristics in at least a partial range of the third region that is next to the at least one of the first region and the second region, the at least a partial range being determined dependent on the each density adjustment value. 2. A density-adjusting device according to wherein the set of reference gamma characteristics further includes; a first reference inflection point corresponding to a point, at which the first reference region connects with the third reference region; and a second reference inflection point corresponding to a point, at which the second reference region connects with the third reference region, and wherein a set of non-reference gamma characteristics for each of at least one density adjustment value further includes: a first inflection point corresponding to a point, at which the first region connects with the third region; a second inflection point corresponding to a point, at which the second region connects with the third regions at least one of the first and second inflection points being shifted from corresponding at least one of the first and second reference inflection points by an amount and in a direction that are determined dependent on the each density adjustment value; an additional inflection point located in the third region, the additional inflection point being the same as a point that is located on the reference monotonous curve as being shifted from the at least one of the first and second reference inflection points along the reference monotonous curve by an amount that is determined dependent on the each density adjustment value; and a monotonous curve that extends between the additional inflection point and the at least one of the first and second inflection points and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the at least one of the first reference inflection point. 3. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include one set of non-reference gamma characteristics for one density adjustment value, wherein the amount of the first region in the set of non-reference gamma characteristics is different from the amount of the first reference region by an amount that is determined dependent on the density adjustment value; wherein the second region in the set of non-reference gamma characteristics is the same as the second reference region; wherein the first inflect-on point in the set of non-reference gamma characteristics is shifted from the first reference inflection point by an amount and in a direction that are determined dependent on the density adjustment value; wherein the second inflection point in the set of non-reference gamma characteristics is the same as the second reference inflection point; wherein the additional inflection point in the set of non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by an amount that is determined dependent on the density adjustment value; wherein the monotonous curve in the set of non-reference gamma characteristics extends between the additional inflection point and the first inflection point and is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and wherein the set of non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the second inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point. 4. A density-adjusting device according to 5. A density-adjusting device according to 6. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include one set of non-reference gamma characteristics for one density adjustment value, wherein the first region in the set of non-reference gamma characteristics is the same as the first reference region; wherein the amount of the second region in the set of non-reference gamma characteristics is different from the amount of the second reference region by an amount that is determined dependent on the density adjustment value; wherein the first inflection point in the set of non-reference gamma characteristics is the same as the first reference inflection point; wherein the second inflection point in the set of non-reference gamma characteristics is shifted from the second reference inflection point by an amount and in a direction that are determined dependent on the density adjustment value; wherein the additional inflection point in the set of non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by an amount that is determined dependent on the density adjustment value; wherein the monotonous curve in the set of non-reference gamma characteristics extends between the additional inflection point and the second inflection point and is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point: and wherein the set of non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the first inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point. 7. A density-adjusting device according to wherein the second region is greater than the second reference region by an amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being greater than an input value at the second reference inflection point by the amount. 8. A density-adjusting device according to wherein the second region is smaller than the second reference region by an amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being smaller than an input value at the second reference inflection point by the amount. 9. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include one set of non-reference gamma characteristics for one density adjustment value, wherein the amount of the first region in the set of non-reference gamma characteristics is different from the amount of the first reference region by a first amount that is determined dependent on the density adjustment value; wherein the amount of the second region in the set of non-reference gamma characteristics is different from the amount of the second reference region by a second amount that is determined dependent on the density adjustment value; wherein the first inflection point in the set of non-reference gamma characteristics is shifted from the first reference inflection point by the first amount and in a first direction that are determined dependent on the density adjustment value; wherein the second inflection point in the set of non-reference gamma characteristics is shifted from the second reference inflection point by the second amount and in a second direction that are determined dependent on the density adjustment value; wherein the additional inflection point in the set of non-reference gamma characteristics includes: a first additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a third amount that is determined dependent on the density adjustment value; and a second additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by a fourth amount that is determined dependent on the density adjustment value; wherein the monotonous curve in the set of non-reference gamma characteristics includes: a first monotonous curve that extends between the first additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the first additional inflection point and the first reference inflection point; and a second monotonous curve that extends between the second additional inflection point and the second inflection point and that is different from a section of the reference monotonous curve between the point the same as the second additional inflection point and the second reference inflection point; and wherein the set of non-reference gamma characteristics further has an additional monotonous curve that extends between the first additional inflection point and the second additional inflection point and that is the same as a section of the reference monotonous curve between the point the same as the first additional inflection point and the point the same as the second additional inflection point. 10. A density-adjusting device according to wherein the first region is greater than the first reference region by the first amount that is determined dependent on the density adjustment value, with an input value at the first inflection point being smaller than an input value at the first reference inflection point by the first amount; and wherein the second region is smaller than the second reference region by the second amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being smaller than an input value at the second reference inflection point by the second amount. 11. A density-adjusting device according to wherein the first region is smaller than the first reference region by the first amount that is determined dependent on the density adjustment value, with an input value at the first inflection point being greater than an input value at the first reference inflection point by the first amount; and wherein the second region is greater than the second reference region by the second amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being greater than an input value at the second reference inflection point by the second amount. 12. A density-adjusting device according to wherein the amount of the first region in the set of non-reference gamma characteristics is different from the amount of the first reference region by a first amount that is determined dependent on the density adjustment value; wherein the amount of the second region in the set of non-reference gamma characteristics is different from the amount of the second reference region by a second amount that is determined dependent on the density adjustment value; wherein the first inflection point in the set of non-reference gamma characteristics is shifted from the first reference inflection point by the first amount and in a first direction that are determined dependent on the density adjustment value; wherein the second inflection point in the set of non-reference gamma characteristics is shifted from the second reference inflection point by the second amount and in a second direction that are determined dependent on the density adjustment value; wherein the additional inflection point in the set of non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a third amount that is determined dependent on the density adjustment value and as being shifted from the second reference inflection point along the reference monotonous curve by a fourth amount that is determined dependent on the density adjustment value; and wherein the monotonous curve in the set of non-reference gamma characteristics includes: a first monotonous curve that extends between the additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and a second monotonous curve that extends between the additional inflection point and the second inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point. 13. A density-adjusting device according to wherein the first region is greater than the first reference region by the first amount that is determined dependent on the density adjustment value, with an input value at the first inflection point being smaller than an input value at the first reference inflection point by the first amount; and wherein the second region is smaller than the second reference region by the second amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being smaller than an input value at the second reference inflection point by the second amount. 14. A density-adjusting device according to wherein the first region is smaller than the first reference region by the first amount that is determined dependent on the density adjustment value, with an input value at the first inflection point being greater than an input value at the first reference inflection point by the first amount; and wherein the second region is greater than the second reference region by the second amount that is determined dependent on the density adjustment value, with an input value at the second inflection point being greater than an input value at the second reference inflection point by the second amount. 15. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include: a set of lightened non-reference gamma characteristics for a lightened density adjustment value, according to which a density of image data is desired to be lightened relative to the predetermined reference density value; and a set of darkened non-reference gamma characteristics for a darkened density adjustment value, according to which a density of image data is desired to be darkened relative to the predetermined reference density value, wherein the first region in the set of lightened non-reference gamma characteristics is greater than the first reference region by a first amount that is determined dependent on the lightened density adjustment value; wherein the second region in the set of lightened non-reference gamma characteristics is the same as the second reference region; wherein an input value at the first inflection point in the set of lightened non-reference gamma characteristics is smaller than an input value at the first reference inflection point by the first amount that is determined dependent on the lightened density adjustment value; wherein the second inflection point in the set of lightened non-reference gamma characteristics is the same as the second reference inflection point; wherein the additional inflection point in the set of lightened non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a first shift amount that is determined dependent on the lightened density adjustment value; wherein the monotonous curve in the set of lightened non-reference gamma characteristics extends between the additional injection point and the first inflection point and is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and wherein the set of lightened non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the second inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point, wherein the first region in the set of darkened non-reference gamma characteristics is the same as the first reference region; wherein the second region in the set of darkened non-reference gamma characteristics is greater than the second reference region by a second amount that is determined dependent on the darkened density adjustment value; wherein the first inflection point in the set of darkened non-reference gamma characteristics is the same as the first reference inflection point; wherein an input value at the second inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the second reference inflection point by the second amount that is deter-mined dependent on the darkened density adjustment value; wherein the additional inflection point in the set of darkened non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by a second shift amount that is determined dependent on the darkened density adjustment value; wherein the monotonous curve in the set of darkened non-reference gamma characteristics extends between the additional inflection point and the second inflection point and is different from a section of tie reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point; and wherein the set of darkened non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the first inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point. 16. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include: a set of lightened non-reference gamma characteristics for a lightened density adjustment value, according to which a density of image data is desired to be lightened relative to the predetermined reference density value; and a set of darkened non-reference gamma characteristics for a darkened density adjustment value, according to which a density of image data is desired to be darkened relative to the predetermined reference density value, wherein the first region in the set of darkened non-reference gamma characteristics is smaller than the first reference region by a first amount that is determined dependent on the darkened density adjustment value; wherein the second region in the set of darkened non-reference gamma characteristics is the same as the second reference region; wherein an input value at the first inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the first reference inflection point by the first amount that is determined dependent on the darkened density adjustment value; wherein the second inflection point in the set of darkened non-reference gamma characteristics is the same as the second reference inflection point; wherein the additional inflection point in the set of darkened non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a first shift amount that is determined dependent on the darkened density adjustment value; wherein the monotonous curve in the set of darkened non-reference gamma characteristics extends between the additional inflection point and the first inflection point and is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and wherein the set of darkened non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the second inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point, wherein the first region in the set of lightened non-reference gamma characteristics is the same as the first reference region; wherein the second region in the set of lightened non-reference gamma characteristics is smaller than the second reference region by a second amount that is determined dependent on the lightened density adjustment value; wherein the first inflection point in the set of lightened non-reference gamma characteristics is the same as the first reference inflection point; wherein an input value at the second inflection point in the set of lightened non-reference gamma characteristics is smaller than an input value at the second reference inflection point by the second amount that is determined dependent on the lightened density adjustment value; wherein the additional inflection point in the set of lightened non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by a second shift amount that is determined dependent on the lightened density adjustment value; wherein the monotonous curve in the set of lightened non-reference gamma characteristics extends between the additional inflection point and the second inflection point and is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point; and wherein the set of lightened non-reference gamma characteristics further has an additional monotonous curve that extends between the additional inflection point and the first inflection point and that is the same as a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point. 17. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include: a set of lightened non-reference gamma characteristics for a lightened density adjustment value, according to which a density of image data is desired to be lightened relative to the predetermined reference density value; and a set of darkened non-reference gamma characteristics for a darkened density adjustment value, according to which a density of image data is desired to be darkened relative to the predetermined reference density value, wherein the first region in the set of lightened non-reference gamma characteristics is greater than the first reference region by a first amount that is determined dependent on the lightened density adjustment value; wherein the second region in the set of lightened non-reference gamma characteristics is smaller than the second reference region by a second amount that is determined dependent or the lightened density adjustment value; wherein an input value at the first inflection point in the set of lightened non-reference gamma characteristics is smaller than the first reference inflection point by the first amount that is determined dependent on the lightened density adjustment value; wherein an input value at the second inflection point in the set of lightened non-reference gamma characteristics is smaller than an input value at the second reference inflection point by the second amount that is determined dependent on the lightened density adjustment value; wherein the additional inflection point in the set of lightened non-reference gamma characteristics includes: a first additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a first shift amount that is determined dependent on the lightened density adjustment value; and a second additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by a second shift amount that is determined dependent on the lightened density adjustment value; wherein the monotonous curve in the set of lightened non-reference gamma characteristics includes: a first monotonous curve that extends between the first additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the first additional inflection point and the first reference inflection point; and a second monotonous curve that extends between the second additional inflection point and the second inflection point and that is different from a section of tie reference monotonous curve between the point the same as the second additional inflection point and the second reference inflection point; and wherein the set of lightened non-reference gamma characteristics further has an additional monotonous curve that extends between the first additional inflection point and the second additional inflection point and that is the same as a section of the reference monotonous curve between the point the same as the first additional inflection point and the point the same as the second additional inflection point, wherein the first region in the set of darkened non-reference gamma characteristics is smaller than the first reference region by a third amount that is determined dependent on the darkened density adjustment value; wherein the second region in the set of darkened non-reference gamma characteristics is larger than the second reference region by a fourth amount that is determined dependent on the darkened density adjustment value; wherein an input value at the first inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the first reference inflection point by the third amount that is determined dependent on the darkened density adjustment value; wherein an input value at the second inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the second reference inflection point by the fourth amount that is determined dependent on the darkened density adjustment value; wherein the additional inflection point in the set of darkened non-reference gamma characteristics includes: a first additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a third shift amount that is determined dependent on the darkened density adjustment value; and a second additional inflection point that is the same as a point that is located on the reference monotonous curve as being shifted from the second reference inflection point along the reference monotonous curve by a fourth shift amount that is determined dependent on the darkened density adjustment value: wherein the monotonous curve in the set of darkened non-reference gamma characteristics includes: a first monotonous curve that extends between the first additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the first additional inflection point and the first reference inflection point; and a second monotonous curve that extends between the second additional inflection point and the second inflection point and that is different from a section of the reference monotonous curve between the point the same as the second additional inflection point and the second reference inflection point; and wherein the set of darkened non-reference gamma characteristics further has an additional monotonous curve that extends between the first additional inflection point and the second additional inflection point and that is the same as a section of the reference monotonous curve between the point the same as the first additional inflection point and the point the same as the second additional inflection point. 18. A density-adjusting device according to wherein the plurality of sets of non-reference gamma characteristics include: a set of darkened non-reference gamma characteristics for a darkened density adjustment value, according to which a density of image data is desired to be darkened relative to the predetermined reference density value; wherein the first region in the set of lightened non-reference gamma characteristics is greater than the first reference region by a first amount that is determined dependent on the lightened density adjustment value; wherein the second region in the set of lightened non-reference gamma characteristics is smaller than the second reference region by a second amount that is determined dependent on the lightened density adjustment value; wherein an input value at the first inflection point in the set of lightened non-reference gamma characteristics is smaller than the first reference inflection point by the first amount that is determined dependent on the lightened density adjustment value; wherein an input value at the second inflection point in the set of lightened non-reference gamma characteristics is smaller than an input value at the second reference inflection point by the second amount that is determined dependent on the lightened density adjustment value; wherein the additional inflection point in the set of lightened non-reference gamma characteristics is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a first shift amount that is determined dependent on the lightened density adjustment value and as being shifted from the second reference inflection point along the reference monotonous curve by a second shift amount that is determined dependent on the lightened density adjustment value; wherein the monotonous curve in the set of lightened non-reference gamma characteristics includes: a first monotonous curve that extends between the additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and a second monotonous carve that extends between the additional inflection point and the second inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point, wherein the first region in the set of darkened non-reference gamma characteristics is smaller than the first reference region by a third amount that is determined dependent on the darkened density adjustment value; wherein the second region in the set of darkened non-reference gamma characteristics is larger than the second reference region by a fourth amount that is determined dependent on the darkened density adjustment value; wherein an input value at the first inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the first reference inflection point by the third amount that is determined dependent on the darkened density adjustment value; wherein an input value at the second inflection point in the set of darkened non-reference gamma characteristics is greater than an input value at the second reference inflection point by the fourth amount that is determined dependent on the darkened density adjustment value; wherein the additional inflection point is the same as a point that is located on the reference monotonous curve as being shifted from the first reference inflection point along the reference monotonous curve by a third shift amount that is determined dependent on the darkened density adjustment value and as being shifted from the second reference inflection point along the reference monotonous curve by a fourth shift amount that is determined dependent on the darkened density adjustment value; wherein the monotonous curve in the set of darkened non-reference gamma characteristics includes: a first monotonous curve that extends between the additional inflection point and the first inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the first reference inflection point; and a second monotonous curve that extends between the additional inflection point and the second inflection point and that is different from a section of the reference monotonous curve between the point the same as the additional inflection point and the second reference inflection point. 19. A density-adjusting device according to wherein the correcting unit corrects the values of the image data by using the set of reference gamma characteristics when the density-adjustment-value setting unit sets the non-adjustment indication. 20. A density-adjusting device according to the selecting unit selecting the set of reference gamma characteristics when the density-adjustment-value setting unit sets the non-adjustment indication, the selecting unit selecting, when the density-adjustment-value setting unit sets the desired density adjustment value, one set of non-reference gamma characteristics that corresponds to the desired density adjustment value, and wherein the correcting unit corrects the values of the image data by using the selected one set of gamma characteristics. 21. A density-adjusting device according to 22. A density-adjusting device according to 23. A density-adjusting device according to wherein the gamma characteristics storing unit is prestored with the set of reference gamma characteristics and is prestored with the plurality of sets of non-reference gamma characteristics in correspondence with a plurality of combinations of the plurality of density adjustment values and a plurality of copy modes, wherein the selecting unit selects the set of reference gamma characteristics when the density-adjustment-value setting unit sets the non-adjustment indication, and selects, when the density-adjustment-value setting unit sets the desired density adjustment value, one set of non-reference gamma characteristics that corresponds to a combination of the desired density adjustment value and the set copy mode. 24. A density-adjusting device according to wherein the gamma characteristics storing unit is prestored with a plurality of sets of reference gamma characteristics in correspondence with the plurality of copy modes and is prestored with the plurality of sets of non-reference gamma characteristics in correspondence with a plurality of combinations of the plurality of density adjustment values and a plurality of copy modes, wherein the selecting unit selects one set of reference gamma characteristics that corresponds to the set copy node when the density-adjustment-value setting unit sets the non-adjustment indication, and selects, when the density-adjustment-value setting unit sets the desired density adjustment value, one set of non-reference gamma characteristics that corresponds to a combination of the desired density adjustment value and the set copy mode. Description 1. Field of the Invention The present invention relates to a density-adjusting device for adjusting the density of image data for an original read by a scanner or the like, and to an image-reading device employing the density-adjusting device. 2. Description of Related Art There is a technology used in copiers that is well known in the art for reading an original image and forming a copy of the image on a recording paper (hereinafter referred to as a “copied image”) at an appropriate density. This technology involves setting reproduction characteristics based on the type of the scanned original and performing correction on the scanned image data using the set reproduction characteristics. For example, a copying device disclosed in U.S. Pat. No. 6,222,640B1 defines reproduction characteristics having a first inflection point (first shoulder point) at the border between a black region and a halftone region and a second inflection point (second shoulder point) on the border between a white region and a halftone region. The copying device of this publication sets one set of reproduction characteristics for binary images, such as texts, and sets another set of reproduction characteristics for multilevel images, such as photographs. The copying device allows an operator to further adjust the first and second inflection points of the reproduction characteristics. It is preferable that a copying device can adjust the density of copied images lighter to reduce noise on the white ground of the copied image or darker to record text more clearly on the copied image, while reproducing halftones with high reproducibility. In view of the foregoing, it is an object of the present invention to provide a density-adjusting device and an image-reading device equipped with the density-adjusting device that are capable of suitably adjusting the density of an image, while reproducing halftones with high reproducibility. In order to attain the above and other objects, the present invention provides a density-adjusting device including: a density-adjustment-value setting unit; a gamma characteristics storing unit; and a correcting unit. The density-adjustment-value setting unit is capable of setting a density adjustment value, according to which a density of image data is desired to be adjusted with respect to a predetermined reference density value. The gamma characteristics storing unit is prestored with a set of reference gamma characteristics in correspondence with the reference density value and is prestored with a plurality of sets of non-reference gamma characteristics in correspondence with a plurality of density adjustment values that can be set by the density-adjustment-value setting unit. The correcting unit corrects values of the image data by using one set of non-reference gamma characteristics that corresponds to the density adjustment value set by the density-adjustment-value setting unit, thereby adjusting the density of the image data according to the desired density adjustment value. The set of reference gamma characteristics includes: a first reference region having first reference characteristics for converting input values to a predetermined maximum output value; a second reference region having second reference characteristics for converting input values to a predetermined minimum output value; and a third reference region defined between the first and second reference regions and having third reference characteristics for converting input values to intermediate output values defined between the maximum output value and the minimum output value, the third reference characteristics defining a reference monotonous curve that changes monotonously with respect to change in the amount of the input value. The set of non-reference gamma characteristics that corresponds to each density adjustment value includes: a first region having first characteristics for converting input values to the maximum output value; a second region having second characteristics for converting input values to the minimum output value; and a third region defined between the first and second regions and having third characteristics for converting input values to intermediate output values defined between the maximum output value and the minimum output value, the third characteristics defining a monotonous curve that changes monotonously with respect to change in the amount of the input value. The amount of at least one of the first region and the second region is different from the amount of the corresponding at least one of the first reference region and the second reference region by a degree that is determined dependent on the each density adjustment value. The third characteristics is different from the third reference characteristics in at least a partial range of the third region that is next to the at least one of the first region and the second region, the at least a partial range being determined dependent on the each density adjustment value. The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiment taken in connector with the accompanying drawings in which: wherein wherein A multifunction device according to a preferred embodiment of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the sane reference numerals to avoid duplicating description. In the following description, the expressions “front”, “rear”, “upper”, “lower”, “right”, and “left” are used to define the various parts when the multifunction device is disposed in an orientation in which it is intended to be used. A multifunction device The multifunction device The multifunction device For the copier function and for a transmitting function in the facsimile function, the multifunction device When desiring to transmit image data for a plurality of sheets of an original document, the scanning operation is repeated the required number of times to scan image data for each of the sheets of the original document while accumulating the image data in memory, and the image data is subsequently transmitted after the transmission confirmation key has been pressed. In the preferred embodiment, each sheet of the original is placed one at a time on the supporting surface manually. However, a well-known mechanism called an automatic document feeder (ADF) may be provided on the multifunction device For the copier function and for a receiving function of the facsimile function, the multifunction device The image-reading unit It is desirable that the multifunction device According to the present embodiment, therefore, a scanning gamma correction unit It is noted that one set of default gamma characteristics is preset in the multifunction device The multifunction device When a user inputs to the multifunction device During the normal copy mode, if the user desires to lighten a copied image with a desired degree from the reference density, the user indicates his/her desire to lighten the copied image by inputting his/her desired lightening degree (which will be referred to as “density adjustment value” hereinafter). In this case, the scanning gamma correction unit On the other hand, if the user desires to darken a copied image with a desired degree from the reference density during the normal copy mode, the user indicates his/her desire to darken the copied image by inputting his/her desired darkening degree (which will also be referred to as “density adjustment value”)). In this case, the scanning gamma correction unit During the highlight/shadow washed-out-appearance correcting copy mode, if the user desires to lighten a copied image with a desired degree from the reference density and indicates his/her desire to lighten the copied image by inputting his/her desired density adjustment value, the scanning gamma correction unit Also during the highlight/shadow washed-out-appearance correcting copy mode, if the user desires to darken the a copied image with a desired degree from the reference density ard indicates his/her desire to darken the copied image by inputting his/her desired density adjustment value, the scanning gamma correction unit During the photograph copy mode, if the user desires to lighten a copied image with a desired degree from the reference density and indicates his/her desire to lighten the copied image by inputting his/her desired density adjustment value, the scanning gamma correction unit Also during the photograph copy mode, if the user desires to darken a copied image with a desired degree from the reference density and indicates his/her desire to darken the copied image by inputting his/her desired density adjustment value, the scanning gamma correction unit Although not shown in the drawings, the multifunction device The display A control section The control section The control section Beneath the directional key More specifically, the center operating button beneath the directional key The menu displayed on the display The directional key As shown in For setting various conditions, the user can display the menu on the display The copy mode can be set in a manner described below. First, the user operates the menu/set button As shown in A text display “Copy Density” at the top of the display screen The currently selected mark In this way, the user can designate his/her desire to adjust the density of copied images to one of seven different stages, including the reference density. Accordingly, the multifunction device The seven types of gamma characteristics for the normal copy mode are shown in FIGS. It is noted that gamma characteristics for the reference density are the same as one another for all the copy modes. In other words, the reference gamma characteristics of FIGS. On the other hand, for each of the six density values other than the reference density value, gamma characteristics of Hence, the gamma characteristics memory Components involved in the copier function include the image-reading unit The controller The density-adjusting unit When an operating button for a main power source as operated to start up the multifunction device When the user displays the density adjustment screen on the display Upon receipt of the newly-set density adjustment value, the controller The image-reading unit In this example, a short edge of the original supporting surface extends in the front-to-rear direction (image-reading main scanning direction), and a long edge of the original supporting surface extends in the left-to-right direction (image-reading sub-scanning direction). The color image sensor extends along the front-to-rear direction (image-reading main scanning direction), and includes; a white light source; a CCD line image sensor capable of reading approximately the same length as the widthwise dimension of an A4-size sheet of paper; and RGE color filters disposed on the exposed surface of the CCD line image sensor. The image-reading unit The image-reading unit The image-processing unit The image-processing unit The shading correction unit The scanning gamma correction unit The color conversion unit In this example, the scanned data is configured of 8-bit data, the maximum density levels V The UCR process unit More specifically, the UCR process unit For example, if the image data for the C color component has she smallest value among the CMY color components, then the UCR process unit The recording gamma correction unit The image-recording unit The image-recording unit The print head is cubic in shape having a prescribed width dimension and includes four nozzles formed in the surface facing the recording paper for ejecting ink of the CMYK colors. Ink cartridges supply ink of the CMYK colors to the respective nozzles. When forming images on the recording paper, the drive controller repeatedly moves the print head reciprocatingly in the main scanning direction over the recording paper at a prescribed rate of speed. The recording controller controls the print head to eject ink of each color onto the recording paper based on recording image data for the CMYK color components at a timing synchronized with the speed at which the print head moves in the main scanning direction, thereby recording one line worth of an image. Each time the print head has recorded one line worth of an image, the recording paper is conveyed exactly one line worth. Thereafter, the operations for recording one line worth of an image with the print head and for conveying the recording paper one line worth are repeated to record the entire image on the recording paper. If a plurality of nozzles is provided in the print head for each color, a plurality of lines can be recorded simultaneously. In such a case, the amount for conveying the recording paper is modified accordingly. Next will be described, with reference to First will be described, with reference to In each graph of the gamma characteristics, the horizontal axis represents input values X, while the vertical axis represents output values Y. Both values have been normalized to have a maximum value of 1.0. It is noted that the maximum value for original, 8-bit image data is 255. In each graph, a region A In the reference gamma characteristics shown in In this example, the density adjustment values for each step in the lighter direction from the default reference density will be called “density−1,” “density−2,” and “density−3.” As shown in In the graph of “density−1,” the waveform of the gamma characteristics in the region less than or equal to the input value corresponding to the point R is identical to the reference gamma characteristics, but the waveform in the region greater than the input value corresponding to the point R differs from the reference gamma characteristics. The difference in the waveform from the reference gamma characteristics is generated by expanding the white region A Therefore, gamma correction performed with the “density−1” characteristics is the same as that performed with the reference density for the halftone portions and black portions of the original document, but makes white portions and near-white portions of the document whiter than gamma correction with the reference density. In this way, the white ground of the original can be made whiter without adversely affecting gamma correction of the scanned data. This gamma correction can prevent black spots or other noise from entering white portions, while appropriately adjusting gradations in halftone areas of the original. Next will be described, with reference to In the comparative method, the white inflection point P is shifted to a lower value P′. The entire part of the waveform of the halftone characteristics M, indicated by a solid line in the drawing, is changed so that the shifted position P′ connects with the fixed black inflection point Q as indicated by a broken line. In this case, the characteristics near the black inflection point Q also change so that the output values will increase rapidly with respect to the input values near the black inflection point Q. Hence, even if the user only wishes to adjust the density so that only the white areas of the image become whiter, all the halftone regions of the image will also be corrected to be whiter, and the contours of the black regions will become more pronounced, producing an image with an overall strong contrast. Gamma characteristics for “density−2” and “density−3” are varied from the reference gamma characteristics according to the same concept used for “density−1.” More specifically, as shown in FIGS. In this way, also for “density−2” and “density−3”, the amount that the white inflection point P is shifted to the new white inflection point P′ parallel to the horizontal axis and the amount that the point R is shifted from the original white inflection point P along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. As shown in More specifically, as the amount of density adjustment from the reference density increases, the gamma characteristics are changed from the reference gamma characteristics so that the white inflection point P is shifted parallel to the horizontal axis to lower values at positions a, b, and c (P′). Further, positions a′, b′, and c′ (R) are provided on the halftone characteristics M corresponding to the respective shifted positions a, b, and c of the white inflection point P, and the reference gamma characteristics are modified so that the shifted position P′ of the white inflection point P is connected to the corresponding point R on the halftone characteristics M, that is, point a is connected to point a′, b to b′, or c to c′. The positions of a′, b′, and c′ corresponding to the positions of a, b, and c, to which the white inflection point P is shifted sequentially, are set to satisfy the expressions Xa′<Xa, Xb′<Xb, and Xc′<Xc, where Xa, Xb, and Xc are input values corresponding to positions a, b, and c and Xa′, Xb′, and Xc′ are input values corresponding to positions a′, b′, and c′. When the white inflection point P is shifted to lower values at positions a and b as the amount of density adjustment from the reference density increases, if the overall waveform of the halftone characteristics M were changed, as indicated by a broken line in However, in the preferred embodiment, as the amount of density adjustment from the reference density increases through “−1” to “−2”, the white region A Here, the position of the point R on the halftone characteristics M is moved from a′ through b′ to c′ downward as the white inflection point P is shifted lower from a through b to c. More specifically, if the point R on the halftone characteristics M were fixed even when the white inflection point P is shifted to a lower value, the slope of the curve connecting the point R on the halftone characteristics M to the shifted position P′ of the white inflection point P would become too great, making the section of the waveform between the shifted point P′ and the point R on the halftone characteristics M differ too greatly from the original waveform of the halftone characteristics M and result in a too much pronounced contrast in the white areas. The present embodiment prevents this by shifting the position of the point R on the halftone characteristics M downward from a′ through b′ to c′ as the position of the white inflection point P′ shifts lower from a through b to c. Accordingly, the rate of change in the slope of the section connecting points P′ and R gradually increases from point P′ to point R. That is, the rate of change in the slope of the section connecting points a and a′ gradually increases from point a to point a′, the rate of change in the slope of the section connecting points b and b′ gradually increases from point b to point b′, and the rate of change in the slope of the section connecting points c and c′ gradually increases from point c to point c′. Since the waveform of the reference gamma characteristics is set in correspondence with the nonlinear reading characteristics of the image-reading unit As shown in As shown in The characteristics for “density+1” are the same as the reference gamma characteristics in the section of the waveform at which the input value is greater than or equal to the input value corresponding to the point S, and differs only in the section of the waveform having a smaller input value than that corresponding to the point S. The waveform is made different from that of the reference gamma characteristics by increasing the black region A Therefore, gamma correction performed with the “density+1” characteristics is the same as that performed with the reference density for the halftone portions and white portions of the original document, but makes black portions and near-black portions of the document more black than gamma correction with the reference density. Accordingly, when adjusting the density in the darker direction, it is possible to make black areas, such as text areas of the original, darker without adversely affecting gamma correction of the scanned data. In other words, black areas can be made more vividly black while appropriately correcting gradations in halftone areas of the original. Next will be described, with reference to In the comparative method, the black inflection point Q is shifted to a higher value Q′. The entire part of the waveform of the halftone characteristics M, indicated by a solid line in the drawing, is changed so that the shifted position Q′ connects with the fixed white inflection point P as indicated by a one-dot-and-one-chain line in In this case, the characteristics near the white inflection point P also change so that the output values will rapidly decrease with respect to the input values near the white inflection point P. Hence, even if the user only wishes to adjust the density so that only the black areas of the image become more black, all the halftone regions of the image will also be corrected to be more black, and the contours of the white regions will become more pronounced, producing an image with an overall strong contrast. Gamma characteristics for “density+2” and “density+3” are modified from the reference gamma characteristics according to the same concept used to modify the gamma characteristics for “density+1.” More specifically, as shown in FIGS. In this way, also for “density+2” and “density+3”, the amount that the black inflection point Q is shifted to the new black inflection point Q′ along the horizontal axis and the amount that the point S is shifted from the black inflection point Q along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. As shown in More specifically, the black inflection point Q is shifted along the horizontal axis to higher values at positions a, b, and c (Q′) as the amount of density adjustment increases, and points a′, b′, and c′ (S) corresponding to the respective shifted positions a, b, and c of the black inflection point Q are provided on the halftone characteristics M. In this way, the reference gamma characteristics are modified so that the shifted position of the black inflection point Q is connected to a corresponding point on the halftone characteristics M. In other words, the reference gamma characteristics are modified to connect points a-a′, b-b′, and c-c′. In this case, positions a′, b′, and c′ on the halftone characteristics M corresponding to positions a, b, and c, to which the black inflection point Q is shifted, are set to satisfy expressions Xa<Xa′, Xb<Xb′, and Xc<Xc′. Hence, as the density adjustment value increases, the slope of the section of the waveform for the halftone characteristics M near the black region is increased, while retaining as much of the waveform of the reference gamma characteristics as possible. When the black inflection point Q is shifted to positions a and b at higher values as the amount of density adjustment increases, if the entire waveform of the halftone characteristics M were changed to connect the shifted positions a and b to the white inflection point P, as indicated by the one-dot-and-one-chain line in However, in the preferred embodiment, as the amount of density adjustment increases through +1 to +2, the black region A Here, the position of the point S on the halftone characteristics M is moved upward as the black inflection point Q is shifted higher for the same reason the position of the point R on the halftone characteristics M is moved downward as the white inflection point P is shifted lower in Specifically, if the point S on the halftone characteristics M were fixed, the slope of the curve connecting the point S on the halftone characteristics M to the shifted position Q′ of the black inflection point Q would become too great, making the section of the waveform between the positions S and Q′ differ too much from the original waveform of the halftone characteristics M and result in a too much pronounced contrast in the black areas. The present embodiment prevents this by shifting the point S or the halftone characteristics M upward to retain as much of the original waveform as possible. Accordingly, the rate of change in the slope of the section connecting points Q′ and S gradually increases from point Q′ to point S. That is, the rate of change in the slope of the section connecting points a and a′ gradually increases from point a to point a′, the rate of change in the slope of the section connecting points b and b′ gradually increases from point b to point b′, and the rate of change in the slope of the section connecting points c and c′ gradually increases from point c to point c′. In the embodiment described above, the density is adjusted from the reference density in three steps for both the lighter and darker directions, but may be set to any desired number of steps. Further, in the embodiment described above, the positions of points R and S on the halftone characteristics M for “density−3” and “density+3” are set equivalent to the black inflection point Q and white inflection point P, respectively, resulting in the entire waveform of the halftone characteristics M becoming different from the halftone characteristics M of the reference gamma characteristics. However, it is unnecessary to greatly modify the white region A Next will be described, with reference to More specifically, the gamma characteristics in As shown in In “density−1” for the highlight/shadow washed-out-appearance correcting copy mode, the waveform of the gamma characteristics for input values greater than or equal to the input value corresponding to the point S are the same as the reference gamma characteristics, but the section of the waveform having smaller input values than that corresponding to the point S is different. This section is made different from the reference gamma characteristics by decreasing the black region A Hence, for the halftone and white portions of the original, gamma correction using the gamma characteristics in “density−1” is performed the same as that with the reference density. However, for black portions and near-black portions of the original, gamma correction using the gamma characteristics in “density−1” restrains the black slightly more than that with the reference density. Accordingly, it is possible to prevent dark colors from erroneously becoming black, without adversely affecting gamma correction of the scanned data. More specifically, when copying originals having text or graphics in dark colors such as blue on a dark background, it is possible to effectively restrain areas of the text or graphics from being converted to black color similar to the ground color. It is therefore possible to prevent the dark text or graphics from appearing washed out and lost in the black shadow background portion. Gamma characteristics for “density−2” and “density−3” are produced by modifying the reference gamma characteristics according to the same concept used for gamma characteristics of “density−1.” More specifically, as shown in FIGS. In this way, also for “density−2” and “density−3”, the amount that the black inflection point Q is shifted to the new black inflection point Q′ along the horizontal axis and the amount that the point S is shifted from the black inflection point Q along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. As shown in Specifically, as the amount of density adjustment increases from the reference density, the black inflection point Q is shifted along the horizontal axis to a lower value at positions a, b, and c (Q′), and points a′, b′, and c′ (S) corresponding to the respective shifted positions a, b, and c of the black inflection point Q are provided on the halftone characteristics M. In this way, the reference gamma characteristics are modified to connect the shifted position of the black inflection point Q to the point on the halftone characteristics M corresponding to the shifted position, that is, to connect points a-a′, b-b′, and c-c′. The positions a′, b′, and c′ on the halftone characteristics M corresponding to the sequentially shifted position of the black inflection point Q are set to satisfy the expressions Xa<Xa′, Xb<Xb′, and Xc<Xc′. As the amount of density adjustment from the reference density increases in the highlight/shadow washed-out-appearance correcting copy mode, the black region A The position of the point S on the halftone characteristics M corresponding to the shifted position Q′ of the black inflection point Q is shifted upward as the shifted black inflection point Q′ is moved to a lower value for the same reason that the position of the point S on the halftone characteristics M is shifted upward as the shifted black inflection point Q′ is moved to a higher value in In In gamma characteristics for “density+1,” the waveform in the region having input values less than or equal to the input value corresponding to the point R is identical to that of the reference gamma characteristics, while the waveform in the region in which the input values are greater than that corresponding to the point R is different. The waveform is made different from the reference gamma characteristics by contracting the white region A Hence, gamma correction for “density+1” is performed the same as for the reference density in the halftone and black areas of the original, but restrains the white slightly more than that of the reference density in white and near-white areas of the original. In this way, when adjusting the density in the darker direction, it is possible to prevent light areas from appearing washed out and lost in white background in the copied image without having adverse effects on gamma correction of the scanned data. For example, when copying original documents having text or graphics in light colors such as yellow on a white background, it is possible to effectively prevent regions of light text and light graphics from being converted to white and washed out or lost in the white ground. Gamma characteristics for “density+2” and “density−3” are generated by modifying the reference gamma characteristics according to the same concept as that used for gamma characteristics for “density+1.” More specifically, as shown in In this way, also for “density+2” and “density+3”, the amount that the white inflection point P is shifted to the shifted point P′ in a direction parallel to the horizontal axis and the amount that the point R is moved from the white inflection point P along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. As shown in Specifically, the white inflection point P is shifted in a direction parallel to the horizontal axis to higher values at positions a, b, and c (P′) as the amount of density adjustment from the reference density increases. Further, points a′, b′, and c′ (R) corresponding to the shifted positions a, b, and c of the white inflection point P are provided on the halftone characteristics M. The reference gamma characteristics are modified to connect the shifted position of the white inflection point P with the point on the halftone characteristics M corresponding to the shifted position, that is, to connect points a-a′, b-b′, and c-c′. Positions a′, b′, and c′ or the halftone characteristics M corresponding to sequentially shifted positions a, b, and c are set to satisfy the expressions Xa′<Xa, Xb′<Xb, and Xc′<Xc. In this case, the waveform for the partial section of the halftone characteristics M near the white region is modified to have a lesser slope as the density adjustment value increases, while retaining as much of the waveform for the halftone characteristics M of the reference gamma characteristics as possible. In the highlight/shadow washed-out-appearance correcting copy mode, the white region A Here, the position of the point R on the halftone characteristics M corresponding to the shifted position P′ of the white inflection point P is moved downward as the shifted position P′ of the white inflection point P is shifted to a higher value for the same reason that the position of the point R on the halftone characteristics M corresponding to the shifted position P′ of the white inflection point P in Next will be described, with reference to As shown in The shifted amount of the white inflection point P to the shifted point P′ parallel to the horizontal axis, the shifted amount of the black inflection point Q to the shifted point Q′ along the horizontal axis, the amount that the point R is moved from the white inflection point P along the halftone characteristics M, and the amount that the point S is moved from the black inflection point Q along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. It is noted that the shifted amount of the white inflection point P to the shifted point P′ and the shifted amount of the black inflection point Q to the shifted point Q′ may be equal to or different from each other. Similarly, the shifted amount of the point R from the point P and the shifted amount of the point S from the point Q may be equal to or different from each other. Gamma characteristics for “density−1” in the photograph copy mode are generated by modifying the waveform of the reference gamma characteristics to include waveform modifications near the white region and waveform modifications near the black region, as described according to FIGS. Since the white region A Gamma characteristics for “density−2” and “density−3” in the photograph copy mode are produced by modifying the reference gamma characteristics according to the same concept used for the gamma characteristics of “density−1.” More specifically, as shown in FIGS. In this way, also for “density−2” and “density−3”, the shifted amount of the white inflection point P to the shifted point P′ parallel to the horizontal axis, the shifted amount of the black inflection point Q to the shifted point Q′ along the horizontal axis, the amount that the point R is moved from the white inflection point P along the halftone characteristics M, and the amount that the point S is moved from the black inflection point Q along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. It is noted that the shifted amount of the white inflection point P to the shifted point P′ and the shifted amount of the black inflection point Q to the shifted point Q′ may be equal to or different from each other. Similarly, the shifted amount of the point R from the point P and the shifted amount of the point S from the point Q may be equal to or different from each other. The gamma characteristics for “density−2” and “density−3” in the photograph copy mode can make white areas whiter, while appropriately maintaining the gradations in halftone areas of a photographic document. On the other hand, gamma characteristics for “density+1” in the photograph copy mode shown in The amount in which the white inflection point P is shifted to the point P′ parallel to the horizontal axis, the amount in which the black inflection point Q is shifted to the point Q′ along the horizontal axis, the distance of the point R from the white inflection point P along the halftone characteristics M, and the distance of the point S from the black inflection point Q along the halftone characteristics M are determined dependent on the amount of density adjustment from the reference density. It is noted that the shifted amount of the white inflection point P to the shifted point P′ and the shifted amount of the black inflection point Q to the shifted point Q′ may be equal to or different from each other. Similarly, the shifted amount of the point R from the point P and the shifted amount of the point S from the point Q may be equal to or different from each other. As with the gamma characteristics for “density−1” in the photograph copy mode, the gamma characteristics for “density+1” are produced by modifying the waveform of the reference gamma characteristics to include waveform modifications in the white region and waveform modifications in the black region. In this case, the white region A Since the gamma characteristics for “density+1” in the photograph copy mode contract the white region A Gamma characteristics for “density+2” and “density+3”in the photograph copy mode are produced by modifying the reference gamma characteristics according to the same concept used for the gamma characteristics of “density+1.” More specifically, as shown in In this way, also for “density+2” and “density+3”, the amount in which the white inflection point P is shifted to the point P It is noted that the shifted amount of the white inflection point P to the shifted point P′ and the shifted amount of the black inflection point Q to the shifted point Q′ may be equal to or different from each other. Similarly, the shifted amount of the point R from the point P and the shifted amount of the point S from the point Q may be equal to or different from each other. Gamma characteristics for “density+2” and “density+3” in the photograph copy mode can adjust densities to make black areas of an image darker, while maintaining appropriate gradations in the halftone areas of a photographic document. Next will be described, with reference to After the density adjustment screen (see If the controller Next, the controller When the user operates the menu/set button In S In S If the controller If the controller Further, if the controller In S After reading an image from an original document, first, in S In S In S In S In S In S In S In S If the image process has not been completed for all lines (S When all lines of the image data have been formed (S In the multifunction device During the normal copy mode, the reference gamma characteristics are modified by expanding the white region A During the highlight/shadow washed-out-appearance correcting copy mode, the multifunction device During the photograph copy mode, the multifunction device While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. For example, in the preferred embodiment described above, the gamma characteristics is defined as a curve in which the output value increases monotonously as the input value increases. However, the gamma characteristics may have the opposite property, that is, gamma characteristics may be defined by a curve in which the output value declines monotonously as the input value increases. The above-described embodiment relates to a copier function of a multifunction device, but may be modified to a wide range of devices that adjust the density of an image by performing gamma correction on image data. Further, the preferred embodiment relates to gamma correction of color images, but may be modified to perform gamma correction on monochrome images. The multifunction device Alternatively, an external digital camera may be connected to the multifunction device In the above description, the black inflection points Q in the reference gamma characteristics of For example, the black inflection points Q in Accordingly, the points P and Q in FIGS. Similarly, the points v and Q in FIGS. Referenced by
Classifications
Legal Events
Rotate |